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That’s Amazing! Worksheet

Poison Frogs: Chytrid Fungus

with Dr. Michael Heithaus

Problem

Do poison dart frogs have anything to worry about? They are not in danger from predators, but their populations are decreasing even in areas that are protected. One hypothesis is that a fungus called chytrid is attacking and killing the frogs. Use the data that Steven and Mike collected to investigate this problem.

Investigation

TO SEE IF CHYTRID MIGHT BE HARMING STRAWBERRY POISON DART FROGS, WE NEED TO FIND OUT (1) IF CHYTRID INFECTS THIS SPECIES, AND (2) IF INFECTED FROGS ARE GETTING SICK. ONE WAY TO FIND OUT IF FROGS ARE HEALTHY IS TO SEE IF THEY WEIGH MORE OR LESS THAN WE WOULD EXPECT FOR A FROG OF THEIR SIZE. AFTER WEIGHING THE FROGS, WE GIVE EACH FROG A “CONDITION SCORE”—FROGS THAT HAVE HIGHER VALUES ARE HEALTHIER AND FROGS THAT HAVE LOWER (NEGATIVE) SCORES ARE SICKER.

Mike and Steven collected ten individuals of several frog species. Table 1 provides data on condition scores and the presence or absence of chytrid fungus for ten individuals of each species.

|Table 1. Infection status and condition of reptiles and amphibians collected at |

|La Selva, Costa Rica |

|Sample |Strawberry poison |Cane toad |Red-eyed tree frog |

| |dart frog | | |

| |Infected? |Condition |Infected? |Condition |Infected? |Condition |

|1 |No |2 |No |–0.5 |No |1 |

|2 |No |1 |No |1 |No |0 |

|3 |No |2 |No |0.5 |No |2 |

|4 |No |0 |No |1 |No |–1 |

|5 |No |1 |No |2 |No |1 |

|6 |Yes |–1 |No |0 |No |–1.5 |

|7 |Yes |–2 |Yes |0 |No |1 |

|8 |Yes |0 |Yes |–0.5 |No |1 |

|9 |Yes |–1 |Yes |2 |No |2 |

|10 |Yes |1 |Yes |1 |Yes |0.5 |

Poison Frogs: Chytrid Fungus continued

1. Data Analysis Calculate the proportion of individuals with infections for each species. Then, calculate the average condition of individuals with and without infections for each species. Place each of these values in Table 2.

|Table 2. Infection rates and average condition factors of three species of frog in La Selva, Costa Rica |

|Species |Percentage of individuals |Average condition score |Average condition score |

| |infected |(infected individuals) |(uninfected individuals) |

|Strawberry poison | | | |

|dart frog | | | |

|Cane toad | | | |

|Red-eyed tree frog | | | |

2. Data Analysis Draw a bar graph demonstrating the percentage of infected individuals for each species.

3. Data Analysis Draw a bar graph of the condition of infected and uninfected individuals of strawberry poison dart frogs.

Poison Frogs: Chytrid Fungus continued

4. Data Analysis Draw a bar graph of the condition of infected and uninfected individuals of cane toads.

5. Data Analysis Draw a bar graph of the condition of infected and uninfected individuals of red-eyed tree frogs.

Poison Frogs: Chytrid Fungus continued

Conclusion

6. IS CHYTRID FUNGUS SOMETHING THAT STRAWBERRY POISON DART FROGS NEED TO WORRY ABOUT? USE YOUR DATA TO SUPPORT YOUR ANSWER.

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7. Are all frogs in the sample infected and affected by chytrid fungus? Use data to support your answer.

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8. Extension Suggest further studies to investigate the impact of chytrid fungus on populations of strawberry poison dart frogs.

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That’s Amazing! Worksheet

Poison Frogs: Leaf Litter

with Dr. Michael Heithaus

Problem

Do poison dart frogs have anything to worry about? They are not in danger from predators, but their populations are decreasing even in areas that are protected. One hypothesis is that a decrease in leaf litter is causing the decline.

A decrease in leaf litter could lead to problems for frogs that live there because the frogs need the moist habitats under the leaves to prevent their skin from drying out and also use it as a place to reproduce.

Use the data that Steven and Mike collected to investigate this problem.

Investigation

TO TEST THE HYPOTHESIS THAT THE AMOUNT LEAF LITTER INFLUENCES THE ABUNDANCE OF STRAWBERRY POISON DART FROGS, STEVEN CREATED AN EXPERIMENT WITH THREE TREATMENTS AND 10 REPLICATES OF EACH TREATMENT (SO HE HAD 30 PLOTS IN ALL). IN ALL 30 PLOTS, STEVEN REMOVED ALL THE LEAVES FROM THE GROUND, THEN HE PUT THE SAME AMOUNT OF LEAF LITTER BACK INTO 10 PLOTS, PUT NO LEAVES BACK INTO 10 PLOTS, AND PUT TWICE AS MANY LEAVES AS HE REMOVED BACK INTO 10 PLOTS. AFTER SIX MONTHS HE CAME BACK TO SEE HOW MANY STRAWBERRY POISON DART FROGS THERE WERE IN EACH PLOT.

1. Identify the constants, independent variable, and dependent variable in Steven’s experiment.

2. Predict which of the three treatments will have the most and the fewest strawberry poison dart frogs, assuming that leaf litter is important for maintaining healthy populations of frogs.

Poison Frogs: Leaf Litter continued

3. Data Analysis Complete Table 1 by calculating the average for

each treatment.

|Table 1. Counts of frogs in different treatments of the leaf litter experiment. |

|Replicate |Strawberry poison dart frogs |

| |No change |Leaves added |Leaves removed |

|1 |5 |10 |2 |

|2 |4 |15 |0 |

|3 |7 |3 |1 |

|4 |4 |18 |1 |

|5 |5 |15 |2 |

|6 |6 |8 |9 |

|7 |16 |12 |0 |

|8 |6 |14 |3 |

|9 |8 |17 |0 |

|10 |6 |11 |2 |

|Average | | | |

4. Data Analysis Draw a graph of the average counts of frogs in each of

the treatments.

Poison Frogs: Leaf Litter continued

Conclusion

5. ARE CHANGES IN THE AMOUNT OF LEAF LITTER A POTENTIAL THREAT TO STRAWBERRY POISON DART FROGS? SUPPORT YOUR ANSWER AND SPECULATE ON WHY THIS RELATIONSHIP OCCURS.

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6. Use the data for strawberry poison dart frogs in Table 1 to argue why it is important to have multiple replicates of each experimental treatment.

7. Extension What other studies might you conduct to investigate the impact of leaf litter on populations of strawberry poison dart frogs?

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8. Extension What other factors that affect populations of strawberry poison dart frogs could you study? How would you test your ideas?

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